ioo TOILERS IN THE SEA. 



stance of the Radiolaria, and assisting in their 

 support. The animal cells furnish the algae with 

 shelter and protection, and also with carbon dioxide, 

 and other products of decomposition, for their nutri- 

 ment, whilst, on the other hand, the vegetable cells 

 of the Xanlhellce yield the Radiolarian its most 

 important supply of nutriment, protoplasm, and 

 starch, as well as oxygen for respiration. It has 

 been experimentally proved that Radiolaria, which 

 contain numerous Xanthellce^ can exist, without 

 extraneous nutriment, for a long period in closed 

 ^vessels of filtered sea-water, kept exposed to the 

 .-sunlight, the two organisms furnishing each other 

 mutually with nourishment. In many Radiolaria 

 the algae are entirely wanting, therefore they are not 

 ..absolutely necessary for existence. 



Circulation is the general term used to express 

 -certain slow currents in the protoplasm, within and 

 without the central capsule, of these organisms. 

 These currents probably continue through the whole 

 life of the animals, and are of great importance for 

 the performance of their vital functions. Sometimes 

 the circulation is directly perceptible in the proto- 

 plasm itself, but it is usually only visible owing to 

 the presence of suspended granules. Although the 

 protoplasm of the inner capsule is in communication 

 with that of the outer, through the openings in the 

 capsular membrane, nevertheless the currents exhibit 



